All Wheel Drive

dmf61

01-20-2008, 12:26 PM

I have a Pontiac Aztec with All Wheel Drive. What controls the activation and deactivation of the syatem. Does it have a transfercase to put power to both front and rear axles? Can the axles run at different speeds? The reason that I am asking is because I am having drivability issue>

Polygon

01-20-2008, 01:43 PM

Yes, it has a transfer case and yes the front and rear can move at different speeds.

Moppie

01-20-2008, 10:31 PM

Yes, it has a transfer case.

I bet it doesn't.

Polygon

01-21-2008, 01:43 AM

I bet it doesn't.

This might sound stupid, but how? Every AWD/4WD vehicle I've ever messed with had a t-case.

Moppie

01-21-2008, 02:42 AM

This might sound stupid, but how? Every AWD/4WD vehicle I've ever messed with had a t-case.

A transfer case is a separate unit mounted to back of a conventional gear box that spits the drive into two directions.
Originally they were completely separate components usually connected by a short lay shaft. Later, they become integrated into the gear box housing, but still use a separate gear set and selector.
You won't find many heavy or light duty 4WDs fitted with them now days though, most use completely integrated gear boxes.

The Aztec, will, like pretty much every AWD car since the Audi Quattro, use an integrated transmission, with everything packed it to a modified version of the FWD gear box.
The drive is already transmitted to the Front wheels the same as a traditional FWD set up, so a third out put is simply fitted that sends drive to the back wheels as well, which is fitted with in the existing housing.

slideways...

01-21-2008, 03:56 PM

true. transfer case is an old word for the housing that held the center diff. the center diff is what splits torque between the front and rear, and in most modern AWD systems is part of the transmission.

KiwiBacon

01-21-2008, 05:34 PM

true. transfer case is an old word for the housing that held the center diff. the center diff is what splits torque between the front and rear, and in most modern AWD systems is part of the transmission.

It's not an old world at all.
It's a part currently used in medium to heavy 4wd vehicles throughout the world, even those being built today.

slideways...

01-21-2008, 06:20 PM

yeah but its still an old word. and is a bad word to use because of all the applications where there is no transfer case. i use center diff to describe it because theres always a center diff no matter how old or new the car/truck is.

KiwiBacon

01-21-2008, 10:28 PM

yeah but its still an old word. and is a bad word to use because of all the applications where there is no transfer case. i use center diff to describe it because theres always a center diff no matter how old or new the car/truck is.
Bollocks.
Many vehicles are part time (aka selectable) 4wd, hence they have a transfer case with no centre diff.
Many other vehicles use a viscous coupling which isn't a differential either.

It isn't an old word and it isn't a bad word. Blaming words when you're struggling with knowledge isn't a good idea.

If the vehicle has a transfer-case then call it a transfer case. If it doesn't then it's the wrong word to use. Same with centre diffs, engines and everything else. Call it what it is.

Moppie

01-21-2008, 11:04 PM

yeah but its still an old word. and is a bad word to use because of all the applications where there is no transfer case.

It is the wrong work to use with reference to the Aztec, as it does not have a transfer case, but that does not make the word bad, nor mean it should not be used.
There are still plenty of vehicles that use transfer cases.

Moppie

01-21-2008, 11:06 PM

put power to both front and rear axles? Can the axles run at different speeds? The reason that I am asking is because I am having drivability issue>

Can you be more specific?
The car will have 3 differentials, one for the front wheels, one for the back wheels, and one for the drive to the rear wheels.
These maybe mechanical, or fluid, and they may be open, limited, or lockable.

Polygon

01-21-2008, 11:09 PM

Ah, that makes sense Moppie. I've just never worked on a vehicle with no t-case. Now, you said the last car with one was the Quattro? My Stealth has a t-case, so does the Evo. I don't know about the Evo X, but I believe all the previous versions do.

Next thing you know they'll put everything in one unit and extend the transmission neck to the rear diff. :lol:

Moppie

01-22-2008, 02:39 AM

My Stealth has a t-case, so does the Evo. I don't know about the Evo X, but I believe all the previous versions do.

I said the first car to not use one was the Quattro :)

What is refered to as the transfer case on the EVO etc, is not really a Transfer case, as it is a fully intergrated part of the gear box.
I think you will find it also house's the front diff.

I've been trying to find a good photo on google, and would you believe there isn't a damn one.

slideways...

01-23-2008, 04:52 PM

Bollocks.
Many vehicles are part time (aka selectable) 4wd, hence they have a transfer case with no centre diff.
Many other vehicles use a viscous coupling which isn't a differential either.

It isn't an old word and it isn't a bad word. Blaming words when you're struggling with knowledge isn't a good idea.

If the vehicle has a transfer-case then call it a transfer case. If it doesn't then it's the wrong word to use. Same with centre diffs, engines and everything else. Call it what it is.

#1 if the car has no center diff, theres no way for the power to get to the other wheels. every car that can have 4 driven wheels has a center diff.

#2 im not sure what you mean by 'viscous coupling' but if you mean a viscous LSD, the D part means differential. if you mean just a coupling that turns the rear wheels or w/e with slippage, there is still a differential. bottom line, the only way to get engine torque turned 90 degrees is with a ring/pinion differential.

GreyGoose006

01-23-2008, 05:13 PM

no. it works like this:

the engine is attached to a FWD transmission, which has an output shaft that can drive the rear wheels as well.

KiwiBacon

01-23-2008, 05:19 PM

#1 if the car has no center diff, theres no way for the power to get to the other wheels. every car that can have 4 driven wheels has a center diff.

#2 im not sure what you mean by 'viscous coupling' but if you mean a viscous LSD, the D part means differential. if you mean just a coupling that turns the rear wheels or w/e with slippage, there is still a differential. bottom line, the only way to get engine torque turned 90 degrees is with a ring/pinion differential.

Looks like you have some learning to do.

The world is full of part-time 4wd vehicles (aka selectable 4wd and 2+2). These vehicles have no centre diff, they drive one end (typically the rear) all the time, the front drive is engaged via clutch or gears. There is no differential action.

A viscous coupling is not a differential, it has no spider gears and does not allow differential motion. They work similar to the scenario above but use a viscous clutch which allows one end to turn at a slightly different speed to the other.
In short one end is fully driven, their is some slip allowed in the other.
Honda have a 4wd system which is hydraulic and probably doesn't use a centre differential either, but I do not know the finer details of that system.

A ring and pinion does not make a differential, to acheive differential action requires typically spider gears or a planetary gearing arrangement.

I suggest you study this topic a little more, you have much to learn.

slideways...

01-23-2008, 06:51 PM

explain to me then how torque is turned 90 degrees? you have to do it to drive both sets of wheels. its unavoidable. oh and when i said ring/pinion diff i was being generic. i meant just a diff that has gears/clutch packs that can turn torque 90 degrees

Steel

01-23-2008, 08:34 PM

In a part time 4wd vehicle, the torque isn't turned 90*. Those are RWD vehicles, and the TRANSFER CASE houses a big strong chain that transfers some (half) of the power driving the rear driveshaft to the front driveshaft. And usually a planetary gearset as well if the vehicle is equipped with a low speed 4wd system. The front and rear output shafts in the transfer case are parallel to each other, no need or want for slip between them.

KiwiBacon

01-23-2008, 10:41 PM

explain to me then how torque is turned 90 degrees? you have to do it to drive both sets of wheels. its unavoidable. oh and when i said ring/pinion diff i was being generic. i meant just a diff that has gears/clutch packs that can turn torque 90 degrees

You really have no idea.
Differential action has nothing to do with turning drive by 90 deg.

Polygon

01-24-2008, 12:57 AM

I said the first car to not use one was the Quattro :)

What is refered to as the transfer case on the EVO etc, is not really a Transfer case, as it is a fully intergrated part of the gear box.
I think you will find it also house's the front diff.

I've been trying to find a good photo on google, and would you believe there isn't a damn one.

Doh! :icon16:

I stand corrected.

Also, for reverence my Stealth has a transaxle, VCU, t-case, and rear diff. It has just about everything. :grinno:

GreyGoose006

01-24-2008, 03:28 PM

Part-time four-wheel-drive systems don't have a differential between the front and rear wheels; instead, they are locked together so that the front and rear wheels have to turn at the same average speed. This is why these vehicles are hard to turn on concrete when the four-wheel-drive system is engaged.
since it is only 4wd part time, and the rest of the time, the wheels spin freely on the axle, it isnt a big issue.
if the car is predominantly fwd, then there is a locking device on the rear wheels
if the car is predominantly rwd, then there is a locking device on the front wheels

Just and FYI, if you do have part time then DON'T engage it on dry pavement unless you want to replace your diff.

KiwiBacon

01-25-2008, 01:06 AM

Just and FYI, if you do have part time then DON'T engage it on dry pavement unless you want to replace your diff.

They are getting stronger though, I've seen a few vehicles that've been run like that for years. Chews the tyres up pretty quick and makes it really hard to steer.

Polygon

01-25-2008, 01:51 AM

They are getting stronger though, I've seen a few vehicles that've been run like that for years. Chews the tyres up pretty quick and makes it really hard to steer.

I guess they got tired of people reporting warranty issues with faulty diffs. :lol:

slideways...

01-26-2008, 06:24 PM

You really have no idea.
Differential action has nothing to do with turning drive by 90 deg.

w/e bad choice of terms. i know how the shit works i just want to know what words you use for the shit. i know differential action is multiplying torque using a gearset but a center differential does the job of powering the other set of wheels from a driveshaft to the (in this case or w/e) front differential. its all called a center diff as far as im concerned. i see what your saying though its more of a transfer case than anything.

KiwiBacon

01-26-2008, 10:57 PM

i know differential action is multiplying torque using a gearset

Actually it's not.

Differential action is allowing two shafts to turn at different speeds but providing the same drive torque to each.

Moppie

01-27-2008, 12:24 AM

w/e bad choice of terms. i know how the shit works

Really? Could have fooled everyone else on the forum.
Or did you forget to put a bull in front of your shit.

GreyGoose006

01-27-2008, 02:52 PM

Really? Could have fooled everyone else on the forum.
Or did you forget to put a bull in front of your shit.

hey, be nice.
he simply broke the first rule of bullshitting.
if you dig yourself a hole cause you dont know what you are talking about, dont try and dig your way out...
digging more will only get you deeper in.
:nono:

slideways...

01-29-2008, 12:25 PM

but i do know what im talking about. i just dont always use the correct terms. but i still passed my ASEs. i think thats what counts...those ASE guys seem to know whats up.

Moppie

01-29-2008, 10:40 PM

but i do know what im talking about. i just dont always use the correct terms. but i still passed my ASEs. i think thats what counts...those ASE guys seem to know whats up.

And there it is.
"But I have a qualification, I must be smart" :rolleyes:

No, sorry. It just proves you have a good memory, and do well under pressure in exams.
As for passing your ASE's, and still not knowing some basic concepts? You might want to have a word with your teachers and take some remedial classes.

Then when you have actually worked on some cars, rebuilt some engines, and have some real, dirt under your finger nails, cuts and bruise and burns experience, then you might begin to understand just how much you don't know.

This is not some little kids forum where knowing how to change the spark plugs and brake pads makes you a god.
Most of the experienced guys here are, or have been, practicing engineers and mechanics, with years and years, and even decades of experience.
Those of us with no or limited professional experience or qualifications still have years of experience rebuilding and working on our own cars, crewing on race teams, building race cars, or working in, or around the automotive industry.
For exmaple I'm one of the least experienced members here, with no formal engineering qualifications, but I have 15 years worth of experience working on everything from a brand new Lotus V8 to a 60ton stationary press.

So quite whining that you do know your talking about, when you keep demonstrating that you don't. Instead sit back, read the threads, ask questions when want to learn more, and go get your hands dirty, and ask more questions when you stumble on something you can't fix.
Then, when you realise you don't it all, and that your qualifications don't really teach you a whole lot, you can come and feel free to give advice on things you do know, because you have first hand experience with them.

KiwiBacon

01-30-2008, 02:55 AM

So in summary, you have to be smart enough to know when you're not smart enough.
You just haven't reached that point yet.